Unexplained sounds from the deep

With Halloween approaching, it’s natural to wonder just a little bit more than usual about things that go “bump” in the night. But what about things that go “bloop” in the deep sea?

Poltergeists, witches and ghosts aren’t the only source for spooky seasonal mystery. In fact, scientists monitoring the oceans have uncovered a handful of sounds that can’t be explained – at least not with any certainty.

With names like “The Bloop,” “Train” and “Julia,” the sounds have been captured by hydrophones, or underwater microphones, monitored by the National Oceanic and Atmospheric Administration (NOAA). Here are the six most mysterious noises ever heard in the sea, and what might have made them. [Listen to the Six Spooky Sounds]

1. The Bloop

The decidedly nonspooky nickname for this sound does little to dispel the mystery surrounding it. In 1997, NOAA hydrophones picked up one of the loudest sounds ever recorded off the southern coast of South America: the Bloop (which sounds like, well, a bloop), was recorded by two hydrophones nearly 3,000 miles (4,800 kilometers) apart.

The Bloop mimics marine animal sounds in some ways, but its volume is too great to be made by any sea creatures known to science. If your imagination is running away from you, you’re not alone: Plenty of listeners have jokingly linked the Bloop to Cthulhu, a fictional part-octopus monster created by sci-fi writer H.P. Lovecraft in 1928.

Deep-sea monsters aside, NOAA holds the most likely explanation for The Bloop is that it was the sound of a large iceberg fracturing. These “icequakes” have been recorded in the Scotia Sea and sound very similar to the mystery 1997 Bloop. If a cracking iceberg were the source, according to NOAA, it would have likely been floating between the Bransfield Strait and the Ross Sea of Antarctica, or perhaps at Cape Adare in East Antarctica.